Distractible intervertebral implant

ABSTRACT

A distractible intervertebral implant configured to be inserted in an insertion direction into an intervertebral space that is defined between a first vertebral body and a second vertebral body is disclosed. The implant may include a first body and a second body. The first body may define an outer surface that is configured to engage the first vertebral body, and an opposing inner surface that defines a rail. The second body may define an outer surface that is configured to engage the second vertebral body, and an inner surface that defines a recess configured to receive the rail of the first body. The second body moves in a vertical direction toward the second vertebral body as the second body is slid over the first body and the rail is received in the recess.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/950,740 filed on Nov. 24, 2015, which is a continuation of U.S.patent application Ser. No. 14/143,529, filed Dec. 30, 2013, which is acontinuation of U.S. patent application Ser. No. 13/170,557, filed Jun.28, 2011, which claims the benefit of U.S. Provision Application Ser.No. 61/359,554, filed Jun. 29, 2010, the contents of all of which arehereby incorporated by reference as if set forth in their entiretyherein.

BACKGROUND

Historically, after complete removal of a disc from between adjacentvertebrae, the adjacent vertebrae were fused together. This “spinalfusion” procedure, which is still in use today, is a widely acceptedsurgical treatment for symptomatic lumbar and cervical degenerative discdisease. More recently, disc arthoplasty may be utilized to insert anartificial intervertebral disc implant into the intervertebral spacebetween adjacent vertebrae. Such a disc implant allows limited universalmovement of the adjacent vertebrae with respect to each other. The aimof total disc replacement is to remove pain generation (caused by adegenerated disc), restore anatomy (disc height), and maintain mobilityin the functional spinal unit so that the spine remains in an adaptedsagittal balance. Sagittal balance is defined as the equilibrium of thetrunk with the legs and pelvis to maintain harmonious sagittal curvesand thus the damping effect of the spine. In contrast with fusiontechniques, total disc replacement preserves mobility in the motionsegment and attempts to mimic physiologic conditions.

SUMMARY

A distractible intervertebral implant configured to be inserted in aninsertion direction into an intervertebral space that is defined betweena first vertebral body and a second vertebral body is disclosed. Theimplant may include a first implant body and a second implant body. Thefirst implant body may define an outer surface that is configured toface the first vertebral body, and an opposing inner surface thatdefines a rail. The second implant body may define an outer surface thatis configured to face the second vertebral body, and an inner surfacethat defines a recess configured to receive the rail of the firstimplant body. The second implant body is configured to move along thevertical direction as the second implant body is translated over thefirst implant body and the rail is received by the recess, so as todistract the first and second vertebral bodies.

In another embodiment, the implant may include a first implant body anda second implant body. The first implant body may include a pair offirst side regions, and may define an outer surface that is configuredto face the first vertebral body. The second implant body may alsoinclude a pair of second side regions. Each second side region may havean anterior end that angles toward the first implant body as theanterior end extends in a direction opposite the insertion direction.The second implant body may define an outer surface that is configuredto face the second vertebral body. The anterior ends of the secondimplant body are configured to contact the first side regions of thefirst implant body as the second implant body is translated over thefirst implant body to thereby cause the outer surface of the secondimplant body to move away from the outer surface of the first implantbody.

In another embodiment, a method for inserting an intervertebral implantinto an intervertebral disc space defined between first and secondvertebral bodies is disclosed. The method may include the step ofinserting a first implant body into the intervertebral space such thatas the first implant body is being inserted at least one of the firstand second vertebral bodies moves away from the other vertebral body.The first implant body may include an outer surface that faces the firstvertebral body, and an inner surface. The method may further includeinserting a second implant body into the intervertebral space by slidingthe second implant body over the inner surface of the first implantbody. The second implant body may cause at least one of the first andsecond vertebral bodies to move away from the other as the secondimplant body is being inserted. The second implant body may include anouter surface that faces the second vertebral body.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofa preferred embodiment of the application, will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the distractable fusion implant and related instruments ofthe present application, there is shown in the drawings a preferredembodiment. It should be understood, however, that the application isnot limited to the precise arrangements and instrumentalities shown. Inthe drawings:

FIG. 1A is a front perspective view of an intervertebral space definedbetween a superior vertebral body and an inferior vertebral body;

FIG. 1B is a front perspective view of a distractible intervertebralimplant inserted into the intervertebral space, the implant including aninferior implant body and a superior implant body;

FIG. 2A is a front perspective view of the inferior implant body of thedistractible fusion implant shown in FIG. 1B;

FIG. 2B is a front elevation view of the inferior implant body shown inFIG. 2A;

FIG. 2C is a side elevation view of the inferior implant body shown inFIG. 2A;

FIG. 2D is a front perspective view of the inferior implant body shownin FIG. 2A with a first fixation member being inserted into a bore ofthe inferior implant body;

FIG. 3A is a bottom perspective view of the superior implant body of thedistractible fusion implant shown in FIG. 1B;

FIG. 3B is a front elevation view of the superior implant body shown inFIG. 3A;

FIG. 3C is a side elevation view of the superior implant body shown inFIG. 3A;

FIG. 3D is a front perspective view of the superior implant body shownin FIG. 3A with a pair of locking screws being inserted into a pair ofbores of the superior implant body;

FIG. 4A is a back perspective view of the superior implant body beingslid onto the inferior implant body;

FIG. 4B is a front perspective view of the superior implant body fullyslid onto the inferior implant body to define the distractible fusionimplant;

FIG. 4C is a front perspective view of the implant shown in FIG. 4B withthree locking screws received within the bores of the superior andinferior implant bodies;

FIG. 4D is a top plan view of the implant shown in FIG. 4C;

FIG. 4E is a cross-sectional view of the implant shown in FIG. 4Dthrough the line 4E-4E;

FIG. 5A is a side elevation view of the inferior implant body being slidinto the intervertebral space defined between the superior and inferiorvertebral bodies to thereby partially distract the vertebral bodies awayfrom each other;

FIG. 5B is a side elevation view of the inferior implant body affixed tothe inferior vertebral body with a first fixation member and a rampportion of the superior implant body contacting an edge of the inferiorimplant body as it is being slid onto the intervertebral space;

FIG. 5C is a side elevation view of the superior implant body furtherslid over the inferior implant body within the intervertebral space; and

FIG. 5D is a side elevational view of the superior implant body affixedto the superior vertebral body with second and third locking screws.

DETAILED DESCRIPTION

Referring to FIG. 1A, an intervertebral space 11 is defined between asuperior vertebral body 12 a and an inferior vertebral body 12 b. Thesuperior vertebral body 12 a generally defines an inferior endplate 13 aor superior surface of the intervertebral space 11, and the adjacentinferior vertebral body 12 b defines a superior endplate 13 b orinferior surface of the intervertebral space 11. Thus, theintervertebral space 11 is disposed between the vertebral bodies 12 aand 12 b. The vertebral bodies 12 a and 12 b can be anatomicallyadjacent vertebral bodies, or can remain after a discectomy has beenperformed that removed a vertebral body from a location between thevertebral bodies. As illustrated, the intervertebral space 11 isillustrated after a discectomy, whereby the disc material has beenremoved or at least partially removed to prepare the intervertebralspace 11 to receive a disc implant that can achieve height restoration.The intervertebral space 11 can be disposed anywhere along the spine asdesired. Moreover, the superior vertebral body 12 a may be considered afirst or a second vertebral body and the inferior vertebral body 12 bmay be considered a first or a second vertebral body.

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “lower” and “upper”designate directions in the drawings to which reference is made. Thewords “inner” or “distal” and “outer” or “proximal” refer to directionstoward and away from, respectively, the geometric center of the implantand related parts thereof. The words, “anterior”, “posterior”,“superior,” “inferior,” “medial,” “lateral,” and related words and/orphrases are used to designate various positions and orientations in thehuman body to which reference is made and are not meant to be limiting.The terminology includes the above-listed words, derivatives thereof andwords of similar import.

Referring also to FIG. 1B, an intervertebral implant, such as adistractable intervertebral implant 10, can be inserted into theintervertebral space 11 along a longitudinal insertion direction I,which can be a posterior direction in accordance with the illustratedembodiment or any other direction as desired. The distractableintervertebral implant 10 is described herein as extending horizontallyalong a longitudinal direction “L” and lateral direction “A”, andvertically along a transverse direction “T”. Unless otherwise specifiedherein, the terms “lateral,” “longitudinal,” and “transverse” are usedto describe the orthogonal directional components of various components.It should be appreciated that while the longitudinal and lateraldirections are illustrated as extending along a horizontal plane, andthat the transverse direction is illustrated as extending along avertical plane, the planes that encompass the various directions maydiffer during use. For instance, when the distractable intervertebralimplant 10 is implanted into the intervertebral space 11 the transversedirection T extends generally along the superior-inferior (orcaudal-cranial) direction, while the plane defined by the longitudinaldirection L and lateral direction A lie generally in the anatomicalplane defined by the anterior-posterior direction, and themedial-lateral direction. Accordingly, the directional terms “vertical”and “horizontal” are used to describe the distractable intervertebralimplant 10 and its components as illustrated merely for the purposes ofclarity and illustration.

Referring to FIG. 1B, the distractable intervertebral implant 10includes a first or inferior implant body 18 and a second or superiorimplant body 14 that is coupled to the inferior implant body 18. Thedistractable intervertebral implant 10 can further include at least onefirst fixation member 22, illustrated as a first screw that couples theinferior implant body 18 to the inferior vertebral body 12 b, and atleast one second fixation member, such as second and third fixationmembers 26 and 30 illustrated as screws, that couple the superiorimplant body 14 to the superior vertebral body 12 a. It should beunderstood that the fixation members 22, 26, and 30 may be also beconfigured as nails, blades, or graft. The distractable intervertebralimplant 10 defines an anterior end 42 and an opposed posterior end 46.The anterior end 42 defines a trailing end of the distractableintervertebral implant 10 along the direction of insertion I, and theposterior end 46 defines a leading end of the distractableintervertebral implant 10 along the direction of insertion I.

The distractable intervertebral implant 10 may be partially or entirelyformed from a metal, polymer, ceramic, allograft, or other artificialbiomaterials such as beta-tricalcium phosphate. Suitable biocompatiblematerials or combinations of materials, may include PEEK, porous PEEK,carbon fiber-reinforced PEEK, titanium and titanium alloys, stainlesssteel, ceramic, polylactic acid, tantalum, magnesium, allograft, orother artificial biomaterials. The distractable intervertebral implant10 presents an outer surface 19 that can be coated with any suitablematerial, such as hydroxyl apatite, beta-tricalcium phosphate, anodicplasma chemical treated titanium, or other similar coatings that improveosseointegration of the distractable intervertebral implant 10. Asshown, the assembled implant 10 may be generally rectangular in shape,though it should be understood that all geometries are imaginable.

Referring to FIGS. 2A-2D the inferior implant body 18 includes a bodyportion 34 that defines a lower or inferior, or outer, engagementsurface 38 configured to contact or otherwise face the superior endplate13 b of the inferior vertebral body 12 b, an opposing inner surface 40,an anterior end 42, and an opposing posterior end 46. The body portion34 further includes a plurality of engagement features 50, illustratedas teeth, that extend transversely out from engagement surface 38 andcan be angled toward the anterior end 42 of the body portion 34. Theengagement features 50 allow the inferior implant body 18 to easilytranslate along a posterior direction over the superior endplate of theinferior vertebral body during insertion of the inferior implant body 18while at the same time provides immediate primary stability allowing theinferior implant body 18 to resist anterior migration. In other words,the engagement features 50 allow the inferior implant body 18 to easilyslide in one direction, but if it were to slide in a second oppositedirection, the teeth 50 would catch on the superior endplate 13 b of theinferior vertebral body 12 b to thereby prevent migration of theinferior implant body 18. It should be understood that the engagementfeatures 50 can be shaped in any manner as desired, such as teeth,spikes, pyramids, cones, undefined geometries, rough surface topography,or independent bodies such a metal spikes that are embedded into thebody portion 34 may be used.

As shown in FIGS. 2A-2D, the body portion 34, such as the inner surface40, includes a middle region 54 and a first side region 58 extendingfrom opposite sides of the middle region 54. The middle region 54protrudes higher in the transverse vertical direction (or outwardlytoward the superior implant body 14) with respect to the first sideregions 58, and thus provides a longitudinally elongate rail that thesuperior implant body 14 can translate longitudinally along. In thisway, the inner surface 40 of the body portion 34 defines the rail. Inaccordance with the illustrated embodiment, the anterior end 62 of themiddle region 54 is angled upwards toward the superior implant body 14as it extends toward the posterior end 46 of the body portion 34, andthe posterior end 66 of the middle region 54 is angled upwards towardthe superior implant body 14 as it extends toward the anterior end 42 ofthe body portion 34. As shown in FIG. 2A, the body portion 34 defines abore 72 that extends through the anterior end 62. As shown in FIG. 2D,the bore 72 is configured to receive the first fixation member 22. Thefirst fixation member 22 can include a shaft 23 and a head 25 that isdimensioned larger than the shaft 23. The bore 72 can likewise include ashaft-receiving region sized to receive the shaft 23, and a headreceiving region sized to receive the head 25 when the fixation member22 is fully received by the bore 72. The bore 72 can further be taperedand elongate along an angle toward the posterior end 46 of the bodyportion 34, such that the fixation member 22 is also elongate along theangle toward the posterior end 46 of the body portion 34 when receivedin the bore 72. The bore 72 can include a locking mechanism that engagea locking mechanism of the first fixation member 22, for instance athread, a locking pin, a ratchet, a rough surface, etc. along one orboth of the shaft 23 and the head 25. It should be understood that atleast one or both of the shaft 23 and the head 25 can be substantiallysmooth and devoid of the locking mechanism. Likewise, at least one orboth of the shaft-receiving region and the head-receiving region can besubstantially smooth and devoid of the locking mechanism.

The middle region 54 further defines a top surface 76 and opposed sidesurfaces 78 that extend down from the top surface 76. The side surfaces78 extend toward each other as they extend down from the top surface 76.That is, as the side surfaces 78 extend down from the top surface 76,the direction in which the side surfaces 78 extend includes a lateralcomponent that extends toward the other side surface 78. Therefore, theside surfaces 78 and the top surface 76 define a dovetail shaped lockingmember. It should be understood, however, that the middle region mayinclude configurations other than a dovetail shaped locking member. Forexample, the middle region may define an L-shaped locking member, agreater angulation longitudinal ratchet, etc.

As shown in FIG. 2A, the first side regions 58 include conical recesses80 at their anterior ends. As shown, the conical recesses 80 are angledup as they extend toward the posterior end 46 of the body portion 34. Aswill be described later, the conical recesses 80 allow the second andthird fixation members 26 and 30 to be inserted into the superiorimplant body 14 of the distractable intervertebral implant 10 at aspecified angle.

The inferior implant body 18 can further include at least one graftwindow 90 such as a plurality of graft windows 90 that extend through atleast one or more of the middle region 54 and the first side regions 58.Generally, each graft window 90 is elongate in the longitudinaldirection, though it should be understood that any shape may be desired.The graft windows 90 are configured to receive autogenous bone graft orbone graft substitute such as Chronos, or DBM. For instance, the graftwindows 90 may be pre-filled with the bone graft.

Referring to FIGS. 3A-3D, and 4A-4E the superior implant body 14 may betranslated, for instance longitudinally, along the inferior implant body18. As shown, the superior implant body 14 includes a body portion 134that defines an upper or superior, or outer, engagement surface 138configured to contact or otherwise face the inferior endplate 13 a ofthe superior vertebral body 12 a, an opposing interior surface 140, ananterior end 142, and an opposing posterior end 146. The body portion134 further includes a plurality of engagement features 150 that extendtransversely out from the engagement surface 138 and can be angledtoward the anterior end 42 of the body portion 134. The engagementfeatures 150 allow the superior implant body 14 to easily translatealong a posterior direction under the inferior endplate of the superiorvertebral body during insertion of the superior implant body 14 while atthe same time provides immediate primary stability allowing the superiorimplant body 14 to resist anterior migration. In other words, theengagement features 150 allow the superior implant body 14 to easilyslide in one direction, but if it were to slide in a second oppositedirection, the engagement features 150 would catch on the inferiorendplate 13 a of the superior vertebral body 12 a to thereby preventmigration of the superior implant body 14. It should be understood thatthe engagement features 150 can be shaped in any manner as desired, suchas teeth, spikes, pyramids, cones, undefined geometries, rough surfacetopography, or independent bodies such a metal spikes that are embeddedinto the body portion 134 may be used.

As shown in FIGS. 3A-3D, the body portion 134, such as the inner surface140, includes second side regions 154 that define a longitudinallyelongate middle recess 158 configured to receive the longitudinallyelongate rail of the body portion 34. The middle recess 158 extends intothe body portion 134 from an inferior side of the superior implant body14, and generally acts as a groove or channel that receives the middleregion 54 of the inferior implant body 18. As shown, the middle recess158 receives the middle region 54 of the inferior implant body 18 as thesuperior implant body 14 translates along the inferior implant body 18.An anterior end 162 of the middle recess 158 defines a conical recess166 that is angled downwards. That is, the anterior end 162 of themiddle recess 158 extends down as it extends toward the posterior end146 of the body portion 134. Additionally, the anterior end 162 of themiddle recess 158 defines a conical recess 166 that angles downward asit extends toward the posterior end 146 of the body portion 134. As willbe described, the conical recess 166 enables the first fixation member22 to be removed from the inferior implant body 18 of the distractableintervertebral implant 10 if so desired.

The middle recess 158 further defines a top surface 168 and opposingside surfaces 170 extending down from the top surface 168. The sidesurfaces 170 extend toward each other as they extend down from the topsurface 168. That is, as the side surfaces 170 extend down from the topsurface 168, the direction in which the side surfaces 170 extendincludes a lateral component that extends toward the other side surface170. Therefore, the side surfaces 170 and the top surface 168 define adovetail shaped channel that receives the dovetail shaped middle region54 of the inferior implant body 18. It should be understood, however,that the middle recess may include configurations other than a dovetailshaped channel. For example, the middle recess may define an L-shapedchannel, a greater angulation longitudinal ratchet, etc.

The second side regions 154 each include an anterior end 172 and aposterior end 176 that are angled downwards. That is, the anterior end172 of the second side regions 154 includes a surface that extend downor otherwise toward the inferior implant body 18 as they extend towardthe posterior end 146 of the body portion 134, and the posterior end 176of the second side regions 154 extend down or otherwise toward theinferior implant body 18 as they extend toward the anterior end 142 ofthe body portion 134. As shown in FIG. 3A, the body portion 134 definesa bore 180 that extends through each anterior end 172. As shown in FIG.3D, each bore 180 is configured to receive one of the second and thirdfixation members 26 and 30. Like the first fixation member 22, thesecond and third fixation members can include a shaft 23 and a head 25that is dimensioned larger than the shaft 23. The bores 180 can likewiseinclude a shaft-receiving region sized to receive the shaft 23, and ahead receiving region sized to receive the head 25 when the fixationmembers 26 and 30 are fully received by the bores 180. The bores 180 canfurther be tapered and elongate along an angle toward the posterior end146 of the body portion 134, such that the fixation members 26 and 30are also elongate along the angle toward the posterior end 146 of thebody portion 134 when received in the bores 180. The bores 180 caninclude locking mechanisms that engage locking mechanisms of the secondand third fixation members 26 and 30, for instance threads, lockingpins, ratchets, rough surfaces, etc. along one or both of the shafts 23and the heads 25. It should be understood that at least one or both ofthe shafts 23 and the heads 25 can be substantially smooth and devoid ofthe locking mechanisms. Likewise, at least one or both of theshaft-receiving regions and the head-receiving regions can besubstantially smooth and devoid of the locking mechanisms.

As shown in FIGS. 3A and 3D, the superior implant body 14 can furtherinclude at least one graft window 190 such as a plurality of graftwindows 190 that extend through at least one or more of the second sideregions 154 as well as through the portion of the body portion 134 inwhich the recess 158 is defined. Generally, each graft window 190 iselongate in the longitudinal direction, though it should be understoodthat any shape may be desired. The graft windows 190 are configured toreceive autogenous bone graft or bone graft substitute such as Chronos,or DBM. For instance, the graft windows 190 may be pre-filled with thebone graft.

As shown in FIG. 3D, the second and third fixation members 26 and 30 maybe inserted into the bores 180 of the superior implant body 14 once thesuperior implant body 14 is fully slid onto the inferior implant body18. The second and third fixation members 26 and 30 extend at an angletoward the posterior end of the distractable intervertebral implant 10.The second and third fixation members 26 and 30 engage the inferiorendplate of the superior vertebral body to thereby securely attach thedistractable intervertebral implant 10 to the superior vertebral body.

As shown in FIGS. 4A-4E, when the superior implant body 14 is fully slidonto the inferior implant body 18, the graft windows 190 of the superiorimplant body 14 align with the graft windows 90 of the inferior implantbody 18. Therefore, the graft windows 90 and 190 define transversechannels that extend through the assembled implant 10. The graft windows190 may be pre-filled with the bone graft.

As shown in FIGS. 4A-4D, the superior implant body 14 lockingly engagesthe inferior implant body 18 with respect to at least one or both ofrelative rotation and relative translation along a direction angularlyoffset with respect to the longitudinal insertion direction I when therecess 158 of the superior implant body 14 has received the rail of theinferior implant body 18. In that regard, the dovetail shaped recess 158of the superior implant body 14 engages the dovetail shaped middleregion 54 of the inferior implant body 18 when the inferior implant body18 is received by the superior implant body 14 to create a form fitbetween the superior and inferior implant bodies 14 and 18. This formfit eliminates rotational degrees of freedom between the superior andinferior implant bodies 14 and 18. Other interlocking features betweenthe superior implant body 14 and the inferior implant body 18 areenvisioned to prevent translation in the longitudinal direction, such asa snap-action mechanism (e.g. PE-inlay or Prodisc-L). A third body (e.g.splint, pin, screw, bolt, glue) that is inserted after intraoperativeassembly of the superior and inferior implant bodies 14 and 18 may alsobe used.

As shown in FIGS. 4C-4E, the bores 72 and 180 are conical in shape. Theconical shaped bores 72, 180 are configured to prevent the fixationmembers 22, 26, and 30 from being over inserted into the bores, andallow for angle stable fixation. The angle stable fixation prevents thefixation members not only from being over inserted but also from backingout. Thus, as each bore 72 and 180 receives its respective fixationmembers 22, 26, and 30 the heads of the fixation members 22, 26, and 30will eventually abut the walls of the bores 72 and 180 to therebyprevent further insertion of the fixation members 22, 26, and 30. Such aconfiguration allows for a more stable fixation of the fixation members22, 26, and 30. Furthermore, the angle stable connection between thefixation member's head and its counter part allow it to bear a bendingmoment.

As shown in FIG. 4E, the distractable intervertebral implant 10 mayinclude marker pins 200, which may be used in case of a radiolucent basematerial that would not be visible in fluoroscopy/x-ray equipment. Asshown, marker pins 200 may be buried within the body portion 34 of theinferior implant body 18. The marker pins 200 may be radioopaque toallow easy identification of the distractable intervertebral implant 10in fluroscopique images. It should be understood that the implant 10 mayinclude any number of pins 200, and that the pins 200 may also be buriedwithin the superior implant body 14. Furthermore, instead of radiopaquemarker pins 200, it may be possible to use polymers, ceramics, orbiomaterials that include barium sulfate, or a similar substance. Bariumsulfate (that is either homogeneously or inhomogeneously distributed inthe base material) allows to make a radiopaque base material visibleunder fluoroscopy/x-ray equipment.

As shown in FIGS. 5A-5D, both the inferior implant body 18 and thesuperior implant body 14 may act as distractors as they are individuallyslid into the intervertebral space 11. As shown, in FIG. 5A, as theinferior implant body 18 is positioned within the intervertebral space11 at least one of the superior vertebral body 12 a and the inferiorvertebral body 12 b moves away from the other such that the superior andinferior vertebral bodies are separated by a first distance F₁. Thefirst distance F₁ may be substantially equal to the transverse height ofthe inferior implant body 18. Once the inferior implant body 18 isproperly positioned and attached to the inferior vertebral body 12 b,the superior implant body 14 may be slid or otherwise translated overthe inferior implant body 18 and into the intervertebral space 11. Asshown in FIG. 5B, the angled posterior ends 176 of the superior implantbody's second side regions 154 contact respective second side regions 58of the inferior implant body 18. Because of the angled posterior ends176 of the superior implant body 14, the superior implant body 14 willmove toward the superior vertebral body 12 a as the superior implantbody 14 is slid over the inferior implant body 18, as shown in FIGS.5B-5D to thereby cause at least one of the superior vertebral body 12 aand the inferior vertebral body 12 b to move away from the other suchthat the vertebral bodies are separated by a second distance F₂ that isgreater than the first distance F₁. In this way, continuous distractionis achieved until the superior implant body 14 is fully assembled withthe inferior implant body 18. As shown in FIG. 5D, the superior implantbody 14 may move a distance H in an upward direction once it has beenfully slid onto the inferior implant body 18. The distance H as well asthe degree of distraction may depend on the angle at which the posteriorends 176 extend toward the anterior end of the superior implant body 14.

In operation, the inferior implant body 18 is first inserted into theintervertebral space. Once properly placed, the first fixation member 22may be inserted into the bore 72 of the inferior implant body 18 anddriven into the inferior vertebral body. Next the superior implant body14 is pushed into the intervertebral space or otherwise slid over theinferior implant body 18. During insertion of the superior implant body14, the superior implant body 14 slides over the inferior implant body18. As described in relation to FIGS. 5A-5D, as the superior implantbody 14 is sliding onto the inferior implant body 18, the superiorimplant body 14 moves up toward the superior vertebral body. Therefore,a continuous distraction of the inferior and superior vertebral bodiesis achieved until the distractable intervertebral implant 10 is fullyassembled. The superior implant body 14 interlocks with the inferiorimplant body 18 and builds a solid construct. The assembled implant 10withstands translation and rotation in all six degrees of freedom.

Once the assembled implant 10 is properly positioned, the second andthird fixation members 26 and 30 may be inserted into the bores 180 ofthe superior implant body 14. The second and third fixation members 26and 30 engage the inferior endplate of the superior vertebral body tothereby securely attach the superior implant body 14 and therefore thedistractable intervertebral implant 10 to the superior vertebral body.

Because the distractable intervertebral implant 10 may be placed intothe intervertebral space 11 by first inserting the inferior implant body18 and then the superior implant body 14, the distractableintervertebral implant 10 may be inserted into the intervertebral space11 either from the anterior end of the patient or from the posterior endof the patient. In other words, by positioning the distractableintervertebral implant 10 in pieces rather than as a fully assembledconstruct the surgeon will be capable of accessing the intervertebralspace 11 from the posterior end of the patient which is usuallydifficult, due to the limited amount of space. It should be understoodthat any surgical approach (i.e. anterior, antero-lateral, lateral,extraforaminal, transforaminal, and posterior) may be considered.

It should be appreciated that the distractable intervertebral implant 10described herein can be configured so as to provide a range of numerouspossible geometries and angular relationships. For example, while thesuperior implant body 14 is described as having angled posterior endsthat cause the superior implant body 14 to move upwards and thereby actas a distractor, it is possible to include an angled anterior end on theinferior implant body 18 to cause the superior implant body 14 todistract as it is inserted. Furthermore, it is envisioned that thesuperior implant body 14 could be inserted into the intervertebral spaceprior to the insertion of the inferior implant body 18.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. Furthermore, it should be appreciated thatthe structure, features, and methods as described above with respect toany of the embodiments described herein can be incorporated into any ofthe other embodiments described herein unless otherwise indicated. It isunderstood, therefore, that this invention is not limited to theparticular embodiments disclosed, but it is intended to covermodifications within the spirit and scope of the present disclosure.

What is claimed:
 1. A method of implanting a distractible intervertebralimplant into an intervertebral space defined between a first vertebralbody and a second vertebral body, the method comprising steps of:inserting first and second implant bodies of the distractibleintervertebral implant into the intervertebral space along an insertiondirection such that an inner surface of the first implant body faces aninner surface of the second implant body, an outer surface of the firstimplant body faces the first vertebral body, and an outer surface of thesecond implant body faces the second vertebral body, the inserting stepcausing at least one of a ramped surface of the first implant body and afirst surface of the distractible intervertebral implant to translatealong another of the ramped surface and the first surface so as to causethe outer surface of at least one of the first and second implant bodiesto move away from the outer surface of another one of the first andsecond implant bodies along a second direction, perpendicular to theinsertion direction; affixing the implant to the first and secondvertebral bodies by (i) inserting a first fixation member through afirst bore defined in the first implant body and into the firstvertebral body, and (ii) passing a second fixation member through afirst recess in the first implant body and then through a second boredefined in the second implant body and into the second vertebral body.2. The method of claim 1, wherein the inserting step causes at least oneof a ramped surface of the second implant body and a second surface ofthe distractible intervertebral implant to translate along the other soas to cause at least one of the outer surfaces of the first and secondimplant bodies to move away from the outer surface of another one of thefirst and second implant bodies along the second direction.
 3. Themethod of claim 1, wherein the affixing step comprises inserting a thirdfixation member through a third bore defined in the second implant bodyand into the second vertebral body.
 4. The method of claim 3, whereinthe affixing step comprises inserting the first to third fixationmembers such that the first fixation member is spaced between the secondand third fixation members with respect to a third direction,perpendicular to both the insertion direction and the second direction.5. The method of claim 1, wherein the affixing step comprises passingthe first fixation member through a second recess in the second implantbody as the first fixation member is inserted into the first bore. 6.The method of claim 1, wherein the first implant body includes a secondramped surface, the second ramped surface being spaced from the rampedsurface of the first implant body along the insertion direction.
 7. Themethod of claim 6, wherein the ramped surface of the first implant bodyand the second ramped surface of the first implant body are angled withrespect to the insertion direction.
 8. The method of claim 6, whereinthe second ramped surface of the first implant body is angled away fromthe first outer surface of the first implant body as the second rampedsurface of the first implant body extends in a direction opposite theinsertion direction.
 9. The method of claim 1, wherein the affixing stepcomprises inserting the first fixation member through the first bore andinto an endplate of the first vertebral body.
 10. The method of claim 9,wherein the affixing step comprises inserting the second fixation memberthrough the second bore and into an endplate of the second vertebralbody.
 11. The method of claim 1, wherein the affixing step comprisesinserting at least one of the first and second fixation members along acentral axis of a respective one of the first and second bores that isangled with respect to the insertion direction.
 12. A method ofimplanting a distractible intervertebral implant into an intervertebralspace defined between a first vertebral body and a second vertebralbody, the method comprising steps of: inserting first and second implantbodies of the distractible intervertebral implant into theintervertebral space along an insertion direction such that an innersurface of the first implant body faces an inner surface of the secondimplant body, an outer surface of the first implant body faces the firstvertebral body, and an outer surface of the second implant body facesthe second vertebral body, the step of inserting the first and secondimplant bodies causing at least one of a ramped surface of the firstimplant body and a first surface of the distractible intervertebralimplant to translate over the other so as to cause the outer surface ofat least one of the first and second implant bodies to move away fromthe outer surface of another one of the first and second implant bodiesalong a second direction, perpendicular to the insertion direction;affixing the first and second implant bodies to the first and secondvertebral bodies by inserting (i) a first fixation member through afirst bore defined in the first implant body and into the firstvertebral body, and (ii) second and third fixation members throughsecond and third bores defined in the second implant body and into thesecond vertebral body, wherein the first to third fixation members areinserted such that the first fixation member is spaced between thesecond and third fixation members with respect to a third direction,perpendicular to both the insertion direction and the second direction.13. The method of claim 12, wherein the first implant body includes asecond ramped surface, the second ramped surface being spaced from theramped surface of the first implant body along insertion direction. 14.The method of claim 13, wherein the ramped surface of the first implantbody and the second ramped surface of the first implant body are angledwith respect to the insertion direction.
 15. The method of claim 13,wherein the second ramped surface of the first implant body is angledaway from the first outer surface of the first implant body as thesecond ramped surface of the first implant body extends in a directionopposite the insertion direction.
 16. The method of claim 12, whereinthe affixing step comprises inserting the first fixation member throughthe first bore and into an endplate of the first vertebral body.
 17. Themethod of claim 16, wherein the affixing step comprises inserting thesecond fixation member through the second bore and into an endplate ofthe second vertebral body.
 18. The method of claim 12, wherein theaffixing step comprises inserting at least one of the first to thirdfixation members along a central axis of a respective one of the firstto third bores that is angled with respect to the insertion direction.19. The method of claim 12, wherein the inserting step comprisestranslating at least one ramped surface of the second implant body alongat least one surface of the distractible intervertebral implant so as tocause the outer surfaces of the first and second implant bodies to moveaway from one another along the second direction.